Oil emerging from the ground at a well-head is pressurized and often includes dissolved gas. It is necessary to separate as much of this gas from the oil as possible before the oil is transported away from the well-head.
Conventionally, an oil-gas separator at a well-head includes a separation tank connected to the well-head, a gas boot connected to the separation tank and a production tank connected to the gas boot. The separation tank and gas boot are connected by lines to a flare stack. The separation tank typically has a capacity of about 11/2 barrels of oil and a production tank a capacity of about 400 barrels. Gas separating from the oil in a production tank cannot enter the flow line to the flare stack because the production tanks have a maximum allowable pressure of about 8 ounces, less than that in the flow line, and any pressure above this is released through a valve to ensure that the tanks do not burst or split from pressure build-up.
These conventional devices suffer the following difficulties:
(a) Due to the design of standard production tanks, vapour break-out is difficult to control, and normally exceeds government regulations. Government monitoring bodies have recognized the difficulty of economically meeting their regulations and have a policy of not enforcing the regulations except in extreme cases.
(b) The exposure of numerous connections to the environment results in increased risk of freeze-up in cold weather, particularly in northern latitudes.
(c) The large number of connections requires extensive set-up and take down procedures often lasting more than a day.
(d) With three tanks, dumping is more difficult, and the interconnections are subject to sludging and general maintenance difficulties.